Perovskite-type composite oxides are composite oxides having a crystal structure of a general formula ABO3 and have been widely used as a ceramic material in various industrial fields.
Of these perovskite-type composite oxides, a perovskite-type composite oxide of a general formula AB(1-y)PdyO3 (y represents an atomic ratio of Pd, the same shall apply hereinafter), in which palladium (Pd) is coordinated on the B site in the crystal structure of the general formula ABO3, shows high catalytic activity as an exhaust gas purifying catalyst (three-way catalyst) that can simultaneously clean up carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx) contained in emissions from internal combustion engines.
Reportedly, as such an exhaust gas purifying catalyst, for example, a perovskite-type composite of La1.00Fe0.57Co0.38Pd0.05O3 suppresses grain growth and maintains high catalytic activity over a long time. This is because of a self-regenerative function, in which the perovskite-type composite oxide reversely introduces or extracts Pd to or from a perovskite-type crystal structure corresponding to oxidation-reduction change of emissions. (See Y. Nishihata et al., Nature, Vol. 418, No. 6894, pp. 164-167, 11 Jul. 2002.)
However, in order to achieve self-regenerative function of Pd of the general formula AB(1-y)PdyO3, it is necessary to form a solid solution of Pd at a high rate in the perovskite-type composite oxide.
On the other hand, even when materials are formulated in the very same amount during the production of the perovskite-type composite oxide of the general formula AB(1-y)PdyO3, there may arise unstable quality in which a solid solution of Pd is sometimes formed at a lower rate. Therefore, it is acutely required to produce a perovskite-type composite oxide in which a solid solution of Pd is formed stably at a high rate.